The first longitudinal, comparative investigation of social structure and development of social behavior in lemurs is proposed. Major objectives are to illuminate the social structures of populations and groups of ringtailed and brown lemurs, and to determine how the behavior of adults and peers in these two societies canalizes development of social behavior in prereproductive individuals toward age- and sex-typical patterns. Because they mature relatively quickly, lemurs are particularly valuable yet untapped resources for research on primate behavioral development. This five-year study will produce behavioral data across prereproductive development for three birth-cohorts (10-15 subjects/cohort) and cross-sectional information from five cohorts of each age-sex class between late infancy and mature adulthood. Systematic behavioral sampling will focus on affinitive and agonistic interactions among juvenile, adolescent, and adult members of two groups of each species. Detailing both structural and contextual features of all social interactions will allow many questions essential to understanding the effects of species identity, age, sex, season, and group size/composition on the development of social behavior to be addressed. All subjects genealogies and histories are known and they live in forested enclosures that provide home ranges of natural size and structure; however, subjects also remain highly accessible for monthly data to be gathered on canine length, body weight, stage of estrus, testicular size and anatomy, and circulating levels of testosterone and cortisol. Several hypothetical relationships between societal and physiological influences on behavioral development will be investigated. Lemur societies represent a second major system of primate social organization and their investigation is a logical and critically important next avenue to pursue in comparative research. Females dominate males in Lemur societies. This female priority is expected to be associated with salient social dynamics not yet known or only partly illuminated for anthropoid primates because thy have not been anticipated or are more subtly expressed in "male-dominated" species. Also, species in which females dominate males provide unique opportunities to test important hypotheses concerning sex roles in society and the development of behavior. Currently, no long-term data are available for any group of prosimians to complement over 25 years of data from cercopithecine monkeys. With such data, coherent arrays of differences/similarities between prosimian, nonhuman anthropoid, and hominid behavior could be discerned that suggest plausible evolutionary changes in primate behavior and identify principles of primate behavioral development.